Matrix again

Since order of multiplication don't matter when you're multiplying three matrices and more ( I deduced this from the multiplication of matrices (AB)C=A(BC) ),
X = IA
X = A
Multiplying A^2 on both sides,
A^2X = A^3
A^2X = I
This is where I'm stuck..

I got the identity matrix for AB.But I do not know how to use it to solve the system of equations, I had applied the identity matric to the system of equations so I got 4a=-8, -2b = 3 and -5c = -15, but this does not seem to be the way..